As it is well known, a fabric is obtained by interweaving two series of threads which are disposed orthogonally one to the other. On the loom, the warp threads are prepared in advance in predetermined number and length, and are longitudinally stretched parallel to each other. Interwoven between the suitably displaced weft threads, and perpendicular thereto, are the warp threads to form thereby the fabric. Formed on the sides of the fabric, to delimit the height thereof, are the two selvages which make up the edges of the same fabric.
The fabrics may be classified in relation to their intended use (clothing, interior design and technical fabrics), as well as to the interlaces that form them and to the elements which contribute to their formation. In this respect, four categories of fabrics may be defined. The simpler fabrics, formed by one warp and one weft, belong to the first category. Belonging to the second category are the fabrics formed by one warp and two or more wefts. The third category includes fabrics with two or more warps. Finally, the fourth category refers to fabrics exhibiting two or more warps and two or more wefts.
In particular, the fabrics of the third category, with two chains and only one series of wefts, have a so-called "underlying" warp intended to link the wefts; the other warp, which has instead the function of achieving either a solid or patterned effect, is called "additional" warp. Since the additional warp has a different evolution from the underlying one, the warping is provided on two distinct beams. Shown in FIG. 7 is the profile of a warp belonging to a fabric of this type, where T indicates the weft, PO the first warp and SO the second warp. It should be noted that the additional warp develops orthogonally to the weft, likewise the underlying warp.